RAID-5 volumes offer data protection at a significant write performance penalty over single disk volumes because of the parity operand reads and parity result writes. The penalty can result in ⅓ to 1/7 the write throughput. There are various strategies for reducing the penalty. One strategy is RAID-1/RAID-5 hybrid which attempts to make the hard working parts of the volume use RAID-1 protection and the rest of the volume use RAID-5. Its drawbacks are the following. RAID-1 is still not as fast as single disk. When data needs to be transferred between the RAID-1 part and RAID-5 part then it incurs even worse performance than just RAID-5. It lessens the capacity of the overall volume.
Another strategy is battery backed up, unpluggable write back cache or write buffer. One drawback to this approach is that few hardware solutions include battery backed up memory and even fewer include unpluggable memory. If the memory is not unpluggable then it lacks the expected RAID-5 protection since a RAID-5 volume's data is expected to survive even if the hardware board itself fails. Unpluggable battery backed cache is short of RAID-5 expectations since the data would be lost if the memory chip itself failed, which is a single point of failure.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art. Accordingly, it is intended that the claimed subject matter be viewed broadly, and be defined only as set forth in the accompanying claims.